Image projection apparatus and method of controlling the same including determining a correction table for correcting RGB values of image data

ABSTRACT

An image projection apparatus that can perform a wall color correction and an ambient light correction obtains a wall color correction parameter by projecting a calibration image for the wall color correction and then obtains an ambient light correction parameter by projecting a calibration image for the ambient light correction, which has been subjected to the wall color correction using the wall color correction parameter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image projection apparatus and amethod of controlling the same.

2. Description of the Related Art

Recently, liquid crystal projectors that can simply and easily display alarge screen by projection have come to be used widely in makingpresentations in meetings or displaying movie content at home. Theliquid crystal projectors are used in various lighting environments, andit is desirable to carry out color reproduction according to actuallighting in projection environments. On the other hand, CIECAM02 (CAM:Color Appearance Model), which is a chromatic adaptation model,published by CIE and other models have been developed for color matchingtechnology. Using these techniques and taking into consideration thelighting environments and the like of liquid crystal projectors, colorreproduction is becoming a possibility.

To apply color reproduction to a liquid crystal projector by taking suchvisual adaptation into consideration, it is necessary to acquireinformation about illuminating light (ambient light) as viewingenvironment information. Existing techniques for measuring suchilluminating light includes, for example, spectroscopic instruments thatuse diffracting gratings and color sensors which use color filters orthe like. Furthermore, it is necessary to install an integrating sphereor diffuser on the front of the sensors in order to sense theilluminating light properly.

Such equipment, if used, will allow the illuminating light to bemeasured accurately, but is not desirable from the viewpoint of productcosts. If the liquid crystal projector is equipped with a screen colormeasurement sensor (color sensor) for automatic screen color correction,desirably the illuminating light is sensed using the color sensor.Examples of measuring illuminating light using a color sensor includes atechnique, described in U.S. Pat. No. 7,314,283, for projecting one ormore calibration images and acquiring color information about the one ormore calibration images using the color sensor. The technique performscolor conversion in such a way as to match appearances of colors basedon color information about an input image and color information aboutthe projected image on a projection plane, thereby changes colors of theinput image, and consequently obtains colors for use to output to theprojector.

The method described in U.S. Pat. No. 7,314,283 measures the calibrationimage in advance and thereby obtains color conversion characteristicswhich realize both color correction on the projection plane andcorrection for the influence of ambient environment light. However,complicated computations are required in order to generate a 3D-LUTwhich realizes both color correction on the projection plane andcorrection for the influence of ambient environment light at the sametime. Furthermore, if ambient illuminating light (ambient light) changesduring projection, it becomes necessary to regenerate the 3D-LUT whichrealizes both color correction on the projection plane and correctionfor the influence of ambient environment light at the same time. Thismakes it necessary to carry out complicated computations again.

SUMMARY OF THE INVENTION

An aspect of the present invention is to eliminate the above-mentionedproblems with the conventional technology.

It is a feature of the present invention to provide an image projectionapparatus and a method of controlling the same which can accurately andquickly generate color correction information for use to correct for theinfluence of ambient environment light even when a projection plane iscolored.

According to an aspect of the present invention, there is provided animage projection apparatus comprising:

an image projection unit configured to project an image on a projectionplane based on image data;

a sensor configured to sense a color on the projection plane; and

a controller configured to control the image projection unit and thesensor and to correct the image data;

wherein the controller makes the image projection unit project a firstimage for a wall color correction, makes the sensor sense color on theprojection plane during projecting the first image, and obtains firstcorrection information based on the sensed color on the projection planeduring projecting the first image,

wherein the controller makes the image projection unit project a secondimage based on image data obtained by correcting the first image for anambient light correction based on the first correction information,makes the sensor sense color on the projection plane during theprojecting the second image, and obtains second correction informationaccording to the sensed color on the projection plane during theprojecting the second image, and

wherein the controller corrects the image data based on the first andsecond correction information and causes the image projection unit toproject an image based on the corrected image data.

Further features and aspects of the present invention will becomeapparent from the following description of exemplary embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a block diagram describing a main configuration of an imageprojection apparatus according to an embodiment of the presentinvention.

FIG. 2 is a diagram showing an application example of the imageprojection apparatus according to the present embodiment.

FIG. 3 is a block diagram describing a configuration of a colorcorrection circuit according to a first embodiment.

FIG. 4 is a flowchart describing operation of the image projectionapparatus according to the first embodiment.

FIG. 5 is a flowchart describing a process performed by an LUTcalculation unit according to the first embodiment.

FIG. 6 is a diagram describing a 3D-LUT for color correction accordingto the first embodiment.

FIG. 7 is a block diagram describing a configuration of a colorcorrection circuit according to a second embodiment.

FIG. 8A is a diagram describing relative spectral sensitivity ofsensors.

FIG. 8B is an rg chromaticity diagram describing a blackbody locus basedon sensitivities of each sensor.

FIG. 9A is a diagram describing a distribution of center values ofstandard light sources in terms of rg chromaticity.

FIG. 9B is a diagram describing major-component information about an Alight source and F12 light source.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will now be described hereinafterin detail, with reference to the accompanying drawings. It is to beunderstood that the following embodiments are not intended to limit theclaims of the present invention, and that not all of the combinations ofthe aspects that are described according to the following embodimentsare necessarily required with respect to the means to solve the problemsaccording to the present invention.

FIG. 1 is a block diagram describing a main configuration of an imageprojection apparatus 100 according to an embodiment of the presentinvention.

The image projection apparatus 100, which is a projection displayapparatus adapted to display an image using a projector, receives avideo signal from an image supply device (not shown) such as a personalcomputer, DVD player, or TV tuner via a connector 101. The video signalis converted into a digital signal by an A/D converter 102. However, ifa digital video signal is received from the image supply device (notshown), the A/D conversion by an A/D converter 102 is unnecessary. Aresolution conversion unit 103 converts the video signal into a videosignal having resolution suitable for red, green, and blue liquidcrystal display devices 107. A color correction circuit 104 appliescolor correction to the video signal whose resolution has been convertedby the resolution conversion unit 103. A display device driving circuit105 performs double-speed conversion, VT gamma correction, and the likeneeded to drive the liquid crystal display devices 107, on the videosignal subjected to color correction, and thereby generates drivesignals for the liquid crystal display devices 107. The liquid crystaldisplay devices 107 receive a luminous flux emitted from an illuminationoptical system 106 and transmit the luminous flux to a projectionoptical system 108 under the control of the drive signals from thedisplay device driving circuit 105. The projection optical system 108performs a zoom operation using a lens 109 and projects the luminousfluxes from each of the liquid crystal display devices 107 onto a screen201 (FIG. 2) as projection light.

A table storage unit 110 implemented by a RAM or the like stores athree-dimensional lookup table (3D-LUT) for ambient light correctioncreated by a lookup table calculation unit (LUT calculation unit) 114. AROM 111 prestores programs executed by a central processing unit (CPU)112, data on the ideal white for the screen 201, and the like. When auser operates a switch 113, switching information is sent to the CPU 112via a data bus 131. The LUT calculation unit 114 performs calculationsto generate a 3D-LUT for color correction through operations describedlater in response to color sensed results produced by a sensor unit 130by sensing colors on the projection plane. The sensor unit 130 includesa red (R) sensor 116, green (G) sensor 117, and blue (B) sensor 118 eachof which has relative spectral sensitivity as shown in FIG. 8A. The CPU112 executes the programs stored in the ROM 111 by loading the programsinto a RAM (not shown) or the like, and thereby controls individualblocks of the image projection apparatus 100.

FIG. 8A is a diagram describing relative spectral sensitivity of eachsensor.

In FIG. 8A, sensor sensitivities are normalized by taking maximumsensitivity of the G sensor 117 as “1” and the relative spectralsensitivities of the R sensor 116, G sensor 117, and B sensor 118 aredesignated by 801, 802, and 803, respectively.

FIG. 8B is an rg chromaticity diagram describing a blackbody locus basedon the sensitivity of each sensor.

Data sensed (measured) by the R sensor 116, G sensor 117, and B sensor118 are converted into digital signals by A/D converters 119, 120, and121, respectively, and sent to a sensor control unit 115. The sensorcontrol unit 115 receives output data from the A/D converters 119, 120,and 121 and converts the output data into a format suitable forprocessing by the CPU 112. Also, the sensor control unit 115 drives thesensor unit 130 on instructions from the CPU 112.

FIG. 2 is a diagram describing an application example of the imageprojection apparatus according to the present embodiment.

The image projection apparatus 100 configured as shown in FIG. 1projects an image from the projection optical system 108 onto the screen201 to produce a projected image 203. At this time the projected image203 is affected by the color of the screen 201 and illuminating light204 emitted from a lighting apparatus 202. For example, even when awhite image is displayed, the image is colored or changes brightnessdepending on the type of screen 201. Color reproduction also varies withthe color temperature and type of the illuminating light 204. The sensorunit 130 detects the brightness and colors of the image on the screen201 to achieve wall color correction and ambient light correction, wherethe wall color correction is correction of color appearance for thecolor of the screen 201 while ambient light correction is the correctionfor color changes caused by the illuminating light 204.

FIG. 3 is a block diagram describing a configuration of the colorcorrection circuit 104 according to a first embodiment.

Output of the resolution conversion unit 103 is inputted in a selector302. Output of a pattern generation circuit 301 which generates acalibration pattern for use to sense the color of the projection planeis also inputted in the selector 302. On instructions from the CPU 112,the selector 302 selects the output of the pattern generation circuit301 when outputting a calibration pattern for use to sense the color ofthe screen 201. On the other hand, when a normal image is projected, theselector 302 selects the output of the resolution conversion unit 103. Acoefficients storage unit 307 stores red gain (Ar), green gain (Ag), andblue gain (Ab) determined by undermentioned operations and received fromthe CPU 112. A multiplier 303 multiplies output of the selector 302 byoutput of the coefficients storage unit 307 and thereby adjusts thegains. Incidentally, although only a single signal line is shown asjoining each pair of components in FIG. 3, this is for the sake ofconvenience, and actually three signal lines may be used for R, G, and Bor a single signal line may be used by time-division multiplexing the R,G, and B. Output of the multiplier 303 is sent to a selector 306 and anaddress generation circuit 304. The address generation circuit 304converts an output signal of the multiplier 303 into an address in thetable storage unit 110 and sends the address to the table storage unit110 via the data bus 131. The table storage unit 110 reads table datawritten in the address received from the address generation circuit 304and sends the table data to a data storage unit 305 via the data bus131. The data storage unit 305 extracts a signal value from the datareceived from the table storage unit 110 and sends the signal value tothe selector 306, where the signal value corresponds to a value obtainedby applying predetermined correction to the output signal of themultiplier 303. On instructions from the CPU 112, the selector 306selects the output of the data storage unit 305 when ambient lightcorrection is performed using the 3D-LUT, and selects the output signalof the multiplier 303 when ambient light correction is not performed.

FIG. 4 is a flowchart describing operation of the image projectionapparatus according to the first embodiment of the present invention. Aprogram which performs this process is stored in the ROM 111, andexecuted under the control of the CPU 112.

The process described in the flowchart is started when power is turnedon or the switch 113 is operated. First in step S402, the imageprojection apparatus 100 generates all-white image data (a first image)using the pattern generation circuit 301 and projects the white colorimage onto the screen 201. The white color image is projected for tworeasons described below. The first reason is that even if the screen 201is colored, by projecting white color image and correcting to display awhite color image on the screen 201, it is possible to eliminate theeffect of coloring of the screen 201 and obtain correct white color onthe screen 201. The second reason is that when bright light such aswhite is projected, light reflected by the screen 201 is affectedgreatly by a light source in the illumination optical system 106,reducing the effect of the illuminating light 204 from the lightingapparatus 202 and thereby making it possible to perform wall colorcorrection without being affected by the illuminating light 204 (ambientlight). Although all-white image data is generated in the exampledescribed above, another color may be used partially, and it is notstrictly necessary to use a completely white color.

At this point, a 3D-LUT for ambient light correction has not beencreated yet, and thus no 3D-LUT is used. Therefore, the selector 306selects the output signal of the multiplier 303. Next, in step S403, theimage projection apparatus 100 acquires color data Rw, Gw, and Bw of thescreen 201 produced by projection of white color, from the R sensor 116,G sensor 117, and B sensor 118, respectively. Next, in step S404, theimage projection apparatus 100 acquires first color data R0, G0, and B0from the ROM 111, where the first color data R0, G0, and B0 representsideal white value stored in the ROM 111. Next, in step S405, the imageprojection apparatus 100 computes gains Ar, Ag, and Ab which willequalize a ratio of Rw, Gw, and Bw of second color data acquired fromthe sensor unit 130 with a ratio of R0, G0, and B0 of the ideal whitevalue acquired in step S404. In the example described above, the gainsAr, Ag, and Ab are computed as correction information throughcalculation of first color correction, that is, wall color correction,and multiplication is performed by the multiplier 303. However, thepresent invention is not limited to this, and another method may be usedalternatively, such as a method which adjusts the gains after matchingblack levels of each color using offset values.

Next, in step S406, the image projection apparatus 100 sends the gainsAr, Ag, and Ab computed in step S405 to the multiplier 303. At the sametime, the pattern generation circuit 301 generates an all-gray pattern(a second image) which is a pattern for sensing of the illuminatinglight 204 and projects the pattern onto the screen 201. The reason why agray image is projected instead of a white image is to accurately sensethe illuminating light 204 reflected by the screen 201 by reducing theeffect of the light source in the illumination optical system 106. Also,at this time, wall color correction is applied to the projected imageusing the gains Ar, Ag, and Ab to eliminate the effect of the coloringof the screen 201. Next, in step S407, the image projection apparatus100 acquires color data Re, Ge, and Be of the screen 201 subjected towall color correction, from the R sensor 116, G sensor 117, and B sensor118, respectively. Incidentally, although an all-gray image is projectedin the example described above, another color may be used partially, ora color other than gray may be used as long as the color contains eachof R, G, and B components.

Next, in step S408, the image projection apparatus 100 substitutes thecolor data Re, Ge, and Be acquired in step S407 into Eqs. (1) and (2)and thereby computes chromaticity of the illuminating light 204.r=Re/(Re+Ge+Be)  Expression (1)g=Ge/(Re+Ge+Be)  Expression (2)

An example of the chromaticity computed here is shown in 810 of FIG. 8B.

Next, in step S409, the image projection apparatus 100 estimates theilluminating light 204 based on the chromaticity computed in step S408.The ROM 111 prestores center values of rg chromaticity andmajor-component information for use to determine likelihood of 15 typesof standard light source—F1 to F12 (fluorescent lamps), A (white lightsource), D50 (5000K), and D65 (daylight). The CPU 112 reads the data forlikelihood determination. Incidentally, although 15 types of standardlight source are used in the present embodiment, naturally more than orless than 15 types of standard light source may be used.

FIG. 9A is a diagram describing a distribution of center values ofstandard light sources in terms of rg chromaticity prestored in the ROM111.

FIG. 9B is a diagram describing major-component information about the Alight source and F12 light source as an example of major-componentinformation. In FIG. 9B, two axes intersecting at right angles at eachcenter value represent major components and an ellipse corresponds to alocus which represents a predetermined likelihood. The CPU 112determines likelihood for all the 15 types of standard light sourcebased on the chromaticity of the illuminating light 204 computed in stepS408 and determines the light source with the highest likelihood asbeing the type of the illuminating light. For example, if thechromaticity of the illuminating light computed in step S408 correspondsto the chromaticity represented by 810 in FIG. 8B and FIG. 9B, the typeof the illuminating light is estimated to be the light source F10.

Next, in step S410, based on the type of the illuminating lightdetermined in step S409, the image projection apparatus 100 performscalculations for second color correction in order for the LUTcalculation unit 114 to generate a 3D-LUT containing color correctioninformation for ambient light correction. The process of creating thethree-dimensional lookup table 3D-LUT in step S410 is performedaccording to a flowchart in FIG. 5.

FIG. 5 is a flowchart describing a process performed by the LUTcalculation unit 114 according to the first embodiment. The process isperformed by the LUT calculation unit 114 on instructions from the CPU112. Prior to this process, 16 kinds of profiles are prepared asdestination profiles and stored in the ROM 111 by measuring screencolors under lighting conditions of F1 to F12, A, D50, and D65 as wellas under a non-lighting condition.

First, in step S502, the LUT calculation unit 114 acquires a set of RGBvalues corresponding to an LUT lattice point. Next, in step S503, theLUT calculation unit 114 converts the acquired RGB values into XYZvalues based on a source device model. The source device model may beone of various models including sRGB and AdobeRGB. Although sRGB is usedas an example of the source device model in the first embodiment, thepresent invention is not limited to this.

Next, in step S504, the LUT calculation unit 114 converts the XYZ valuescomputed in step S503 into JCh values based on CIECAM02 published by theCommission Internationale de l'Eclairage (CIE; or the InternationalLighting Commission). Next, in step S505, based on a source color gamutand destination color gamut, the LUT calculation unit 114 does colorgamut mapping so as to map colors outside the destination color gamut toa destination color gamut surface with the shortest distance withoutconverting colors in the destination color gamut. The source color gamutand destination color gamut are computed in advance before this process.Next, in step S506, the LUT calculation unit 114 converts the JCh valuescomputed in step S504 into XYZ values based on CIECAM02. Next, in stepS507, the LUT calculation unit 114 converts the XYZ values computed instep S506 into RGB values based on a destination device model.Incidentally, the destination profile used in step S507 is selected fromthe 16 kinds of profiles described above. In S508, the LUT calculationunit 114 determines whether conversion into RGB values has beencompleted at all LUT lattice points. If computations of RGB values havebeen completed, the LUT calculation unit 114 advances the process tostep S509. Otherwise, the process returns to step S502. In step S509,the LUT calculation unit 114 stores the 3D-LUT for conversion in thetable storage unit 110, and finishes processing.

Once the processing is finished, the image projection apparatusaccording to the present embodiment is ready to project an imageobtained by applying ambient light correction and wall color correctionto the inputted image data.

FIG. 6 is a diagram describing a 3D-LUT for color correction accordingto the first embodiment.

Specifically, FIG. 6 shows combinations of color coordinate data oflattice points in an RGB color space and RGB values which are latticepoint data associated with RGB coordinate values of the lattice points.Although FIG. 6 shows an example in which RGB data is 10 bits andlattice points are located at points obtained by dividing each of the R,G, and B axes into eight equal parts, the bit count of signals and thenumber of lattice points are not limited to these.

In the flowchart in FIG. 5, each of the lattice points (R,G,B)=(0, 0, 0)to (R,G,B)=(1023, 1023, 1023) is subjected to the processes of stepsS502 to S507 to generate a 3D-LUT for ambient light correction.Post-conversion RGB values other than those of the lattice points aregenerated by an interpolation process.

In the first embodiment, the LUT calculation unit 114 is provided togenerate a 3D-LUT on a hardware basis on instructions from the CPU 112as an example. However, the method for generating a 3D-LUT is notlimited to this, and the CPU 112 may generate a 3D-LUT throughcalculations according to software instead of using the LUT calculationunit 114. Anyway, there is no difference between hardware and softwarein that the image projection apparatus operates according to theflowcharts in FIGS. 4 and 5.

In the first embodiment, the LUT calculation unit 114 generates the3D-LUT for ambient light correction based on the type of illuminatinglight determined. However, the present invention is not limited to this,and 3D-LUTs for each type of illuminating light may be prestored in theROM 111 to allow selection of the 3D-LUT corresponding to theilluminating light determined in step S410 in FIG. 4.

As described above, according to the first embodiment, the imageprojection apparatus first senses the color of the projection planeusing a sensor, then performs screen color correction (wall colorcorrection), does a projection, senses the color of the projection planeusing a sensor again in this state, and estimates illuminating light(ambient light). This makes it possible to estimate the illuminatinglight accurately even if the screen is colored and furthermore toaccurately generate a 3D-LUT for illuminating light correction based onthe estimated illuminating light.

Also, in generating the 3D-LUT, since it is only necessary to create atable which is used only for correction for illuminating light and whichdoes not have a wall color correction function, it is possible to reducecalculation time. Furthermore, even if the type or state of illuminatinglight changes during projection, since the wall color correction hasbeen completed in the previous state of the illuminating light, a 3D-LUTfor illuminating light correction can be generated accurately byestimating the illuminating light quickly.

A second embodiment of the present invention will be now described withreference to FIG. 7. The image projection apparatus according to thesecond embodiment has the same configuration (FIG. 1) as the imageprojection apparatus according to the first embodiment, and thusdescription thereof will be omitted. The difference is that whereas gainadjustment is used for wall color correction in the first embodimentdescribed above, a one-dimensional lookup table (1D-LUT) is used forwall color correction in the second embodiment. To generate the 1D-LUT,a basic 1D-LUT may be stored in the ROM 111, and changes incharacteristics may be made by the LUT calculation unit 114 as a resultof wall color correction and stored in the table storage unit 110.Alternatively, the 1D-LUT may be generated from scratch by the LUTcalculation unit 114 and sent to the table storage unit 110. Then, the1D-LUT is stored in a different area of the table storage unit 110 fromthe 3D-LUT for ambient light correction.

The generation or change of the 1D-LUT is done in step S405 of theflowchart in FIG. 4. Here, a ratio of R, G, and B of 1D-LUT outputvalues is set to be R0:G0:B0. Normally, the 1D-LUT is used for gammacorrection. The gamma correction may be replaced by the VT gammacorrection performed by the display device driving circuit 105 accordingto the first embodiment described above or may be performed using γ=2.2.

FIG. 7 is a block diagram describing a configuration of a colorcorrection circuit 104 according to the second embodiment.

Output of the resolution conversion unit 103 is inputted in the selector302. Output of a pattern generation circuit 301 which generates acalibration pattern for use to sense the projection plane is alsoinputted in the selector 302. On instructions from the CPU 112, theselector 302 selects the output of the pattern generation circuit 301when a calibration pattern for color measurement of the screen 201 isused, and selects the output of the resolution conversion unit 103 whena normal image is projected. Output of the selector 302 is sent to aselector 310 and an address generation circuit 308. The addressgeneration circuit 308 converts an output signal of the selector 302into an address in the table storage unit 110 and sends the address tothe table storage unit 110 via the data bus 131. The table storage unit110 reads data out of the inputted address and sends the data to a datastorage unit 309 via the data bus 131. The data storage unit 309extracts a signal value from the data received from the table storageunit 110 and sends the signal value to the selector 310, where thesignal value corresponds to a value obtained by applying predeterminedcorrection to the output signal of the selector 302. The addressgeneration circuit 308 and data storage unit 309 exchange addresses anddata related to the 1D-LUT. On instructions from the CPU 112, theselector 310 selects the output signal of the data storage unit 309 whenwall color correction is performed using the 1D-LUT, and selects theoutput signal of the selector 302 when the wall color correction is notperformed using the 1D-LUT.

Output of the selector 310 is sent to a selector 306 and an addressgeneration circuit 304. The address generation circuit 304 converts anoutput signal of the selector 310 into an address in the table storageunit 110 and sends the address to the table storage unit 110 via thedata bus 131. The table storage unit 110 reads data out of the inputtedaddress and sends the data to the data storage unit 305 via the data bus131. The data storage unit 305 extracts a signal value from the datareceived from the table storage unit 110 and sends the signal value tothe selector 306, where the signal value corresponds to a value obtainedby applying predetermined correction to the output signal of theselector 310. The address generation circuit 304 and a data storage unit305 exchange addresses and data related to the 3D-LUT. On instructionsfrom the CPU 112, the selector 306 selects the output of the datastorage unit 305 when ambient light correction is performed using the3D-LUT, and selects the output signal of the selector 310 when ambientlight correction is not performed.

As described above, according to the second embodiment, the imageprojection apparatus first senses the color of the projection planeusing a sensor, then performs screen color correction (wall colorcorrection) using a 1D-LUT, does a projection, senses the color of theprojection plane using the sensor again in this state, and therebyestimates illuminating light (ambient light). This makes it possible toestimate the illuminating light accurately even if the screen is coloredand furthermore to accurately generate a 3D-LUT for illuminating lightcorrection based on the estimated illuminating light.

Also, in generating the 3D-LUT, since it is only necessary to create atable which is used only for illuminating light correction and whichdoes not have a wall color correction function, it is possible to reducecalculation time. Furthermore, even if the type or brightness ofilluminating light changes during projection, since wall colorcorrection has been completed in the previous state of the illuminatinglight, a 3D-LUT for illuminating light correction can be generatedaccurately by estimating the illuminating light quickly.

Aspects of the present invention can also be realized by a computer of asystem or apparatus (or devices such as a CPU or MPU) that reads out andexecutes a program recorded on a memory device to perform the functionsof the above-described embodiment(s), and by a method, the steps ofwhich are performed by a computer of a system or apparatus by, forexample, reading out and executing a program recorded on a memory deviceto perform the functions of the above-described embodiment(s). For thispurpose, the program is provided to the computer for example via anetwork or from a recording medium of various types serving as thememory device (e.g., computer-readable medium).

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2009-157313, filed Jul. 1, 2009, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image projection apparatus comprising: anobtain unit that obtains image data; a first correction unit, thatcorrects the image data obtained by the obtain unit; a second correctionunit that corrects the image data corrected by the first correctionunit; an image projection unit that projects an image <on a projectionplane based on image data; a sensor that senses a color on theprojection plane; and a controller; wherein the controller controls theimage projection unit to project a white color image on the projectionplane, wherein the white color image is not corrected by the firstcorrection unit and the second correction unit, and controls to causethe sensor to perform a first sensing in which the sensor senses theprojection plane on which the white color image is projected, whereinthe controller computes a gain of the first correction unit based onboth data of the white color image sensed in the first sensing and anideal white color value of the white color image, wherein he controllercontrols to cause the first correction unit to correct a gray colorimage by using the gain, controls the image projection unit to projectthe gray color image corrected by the first correction unit on theprojection plane, and controls to cause the sensor to perform a secondsensing in which the sensor senses the projection plane on which thegray color image is projected, wherein the controller computes achromaticity based on a sensed result of the second sensing, wherein thecontroller estimates a type of light source in an environment in whichthe image projection apparatus is located, based on the chromaticity,and wherein the controller determines a correction table for correctingRGB values of image data input in the second correction unit inaccordance with the type of the light source.
 2. The image projection,apparatus according to claim 1, wherein the first correction unitcorrects the image data by using a one-dimensional lookup table.
 3. Theimage projection apparatus according to claim , wherein the secondcorrection unit corrects the image by using a one-dimensional lookuptable.
 4. The image projection apparatus according to claim 1, whereinthe controller controls the first correction unit to correct the graycolor image by using a gamma correction, wherein the gamma correctionbeing for approximating RGB values of the first sensing to RGB values ofthe white color image.
 5. The image projection apparatus according toclaim 1, wherein the controller controls the first correction unit tocorrect the gray color image by using a gain adjustment, wherein thegain adjustment being for approximating RGB values of the first sensingto RGB values of the white color image.
 6. The image projectionapparatus according to claim 1, wherein the controller controls thefirst correction unit to correct the image, data obtained by the obtainunit, controls the second correction unit to correct the image datacorrected by the first correction unit, and controls the projection unitto project the image data corrected by the second correction unit.
 7. Amethod of controlling an image projection apparatus which includes animage projection unit and an image sensing unit, comprising: an obtainstep of obtaining image data; a first correction step of correcting theimage data obtained in the obtain step; a second correction step ofcorrecting the image data corrected in the first correction step; animage projection step of projecting an image on a projection plane basedon image data; a sensing step of causing a sensor to sense a color onthe projection plane; and a control step of controlling: (i) to projecta white color image on the projection plane, wherein the white colorimage is not corrected in the first correction step and the secondcorrection step, and to perform a first sensing in which the sensorsenses the projection plane on which the white color image is projected,(ii) to compute a gain of the first correction step based on both dataof the white color image sensed in the first sensing and an ideal whitecolor value of the white color image, (iii) to cause the firstcorrection step to correct a gray color image by using the gain, projectthe gray color image corrected in the first correction step on theprojection plane, and to cause the sensor to perform a second sensing inwhich the sensor senses he projection plane on which the gray colorimage is projected, (iv) to compute a chromaticity based on a sensedresult of the second sensing, (v) to estimate a type of light source inan environment in which the image projection apparatus is located, basedon the chromaticity, and (vi) to determine a correction table forcorrecting RGB values of image data input in the second correction stepin accordance with the type of the light source.
 8. An image projectionapparatus comprising: an obtain unit that obtains image data; a firstcorrection unit that corrects the image data obtained by the obtainunit; a second correction unit that corrects the image data corrected bythe first correction unit; an image projection unit that projects animage on, a projection plane based on image data; a sensor that senses acolor on the projection plane; and a controller; wherein the controllercontrols the image projection unit to project a white color image,wherein the white color image is not corrected by the first correctionunit and the second correction unit, controls the sensor to sense coloron the projection plane during projecting the white color image on theprojection plane, and obtains first correction information in accordancewith the sensed color on the projection plane and an ideal white colorvalue of the white color image, wherein after obtaining the firstcorrection information the controller controls the first correction unitto correct a gray color image, based on the first correctioninformation, controls the image projection unit to project the graycolor image corrected by the first correction unit on the projectionplane, controls the sensor to sense color on the projection plane duringprojecting the gray color image, estimates a type of light source in anenvironment in which the image projection apparatus is located, based ona chromaticity of the sensed color on the projection plane, and obtainssecond correction information in accordance with the type of lightsource in an environment in which the image projection apparatus islocated, and wherein the controller corrects the image data based on thefirst correction information and the second correction information andcauses the image projection unit to project the corrected image.
 9. Animage projection apparatus comprising: an image projection unit thatprojects an image on a projection plane based on image data; an imagesensing unit that senses color on the projection plane; a wall colorcorrection unit; an ambient light correction unit; and a controller,wherein he controller controls the image projection unit to project awhite color image for a wall color correction, wherein the white colorimage is not corrected by the wall color correction unit and the ambientlight correction unit, and obtains wall color correction informationbased on sensed results produced by the image sensing unit when thewhite color image is projected and an ideal white color value of thewhite color image, and wherein the controller controls the projectionunit to project a gray color image for an ambient light correction,wherein the gray color image data is corrected based on the wall colorcorrection information by the wall color correction unit, estimates atype of ambient light based on a chromaticity of the sensed results onthe projection plane, and obtains ambient light correction informationbased on the estimated type of ambient light.
 10. The image projectionapparatus according to claim 9, wherein the wall color correctioninformation is stored as a one-dimensional lookup table.
 11. The imageprojection apparatus according to claim 9, wherein the ambient lightcorrection information is stored as a three-dimensional lookup table.12. The image projection apparatus according to claim 9, wherein thecontroller computes the wall color correction information such that aratio of Rw, Gw, and Bw of the sensed results will approach a ratio ofR0, G0, and B0 of the ideal white color value.
 13. A method ofcontrolling an image projection apparatus having an image projectionunit for projecting an image on a projection plane, an image sensingunit for detecting a color of the projection plane, a wall colorcorrection unit, and an ambient light correction unit, comprising: acontrol step of: (i) controlling the image projection unit to project awhite color image for a wall color correction, wherein the white colorimage is not corrected by the wall color correction unit and the ambientlight correction unit, and obtaining wall color correction informationbased on sensed results produced by the image sensing unit when thewhite color image is projected and an idea white color value of thewhite color image, (ii) controlling the projection unit to project agray color image for an ambient light correction, wherein the gray colorimage is corrected based on the wall color correction information by thewall color correction unit, estimating a type of ambient light based ona chromaticity of the sensed results on the projection plane, andobtaining ambient light correction information based on the estimatedtype of ambient light.